问题描述

我很肯定下面的 swift 代码已经涵盖了所有可能性，但 Xcode 一直告诉我，切换必须是详尽的，考虑添加一个默认子句."

I am positive that the following swift code has covered all possibilities, but Xcode keeps telling me that, "Switch must be exhaustive, consider adding a default clause."

谁能告诉我我错过了什么?谢谢.

Can anyone tell me what did I miss? Thanks.

let a = false
let b = false
let c = false

func test(a: Bool, _ b: Bool, _ c: Bool) {
    switch (a, b, c) {
    case (true, false, _):
        print("Moved left!!!")
    case (true, true, _):
        print("Moved right!!!")
    case (false, _, false):
        print("Moved up!!!")
    case (false, _, true):
        print("Moved down!!!")
    // Error: Switch must be exhaustive, consider adding a default clause.
    }
}

test(false, false, false)
test(false, false, true)
test(false, true, false)
test(false, true, true)
test(true, false, false)
test(true, false, true)
test(true, true, false)
test(true, true, true)

推荐答案

编译器无法对您的模式下结论，因为它太复杂或太不寻常.如果您的模式会更规律，例如:

The compiler is unable to conclude about your pattern because it is too complex or too unusual for it. If your pattern would have been more regular like:

case (true, false, _):
    print("Moved left!!!")
case (true, true, _):
    print("Moved right!!!")
case (false, false, _):
    print("Moved up!!!")
case (false, true, _):
    print("Moved down!!!")

那么编译器就不会抱怨了.在这种情况下，它很容易得出您涵盖所有情况的结论.

then the compiler would have not complained. It that case it is easy for it to conclude that you covered all the cases.

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